RESUMEN
Effluents from wastewater treatment plants (WWTPs) containing micro-organisms and residual nitrogen can stimulate nitrification in freshwater streams. We hypothesized that different ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria present in WWTP effluents differ in their potential to colonize biofilms in the receiving streams. In an experimental approach, we monitored biofilm colonization by nitrifiers in ammonium- or nitrite-fed microcosm flumes after inoculation with activated sludge. In a field study, we compared the nitrifier communities in a full-scale WWTP and in epilithic biofilms downstream of the WWTP outlet. Despite substantially different ammonia concentrations in the microcosms and the stream, the same nitrifiers were detected by fluorescence in situ hybridization in all biofilms. Of the diverse nitrifiers present in the WWTPs, only AOB of the Nitrosomonas oligotropha/ureae lineage and NOB of Nitrospira sublineage I colonized the natural biofilms. Analysis of the amoA gene encoding the alpha subunit of ammonia monooxygenase of AOB revealed seven identical amoA sequence types. Six of these affiliated with the N. oligotropha/ureae lineage and were shared between the WWTP and the stream biofilms, but the other shared sequence type grouped with the N. europaea/eutropha and N. communis lineage. Measured nitrification activities were high in the microcosms and the stream. Our results show that nitrifiers from WWTPs can colonize freshwater biofilms and confirm that WWTP-affected streams are hot spots of nitrification.
Asunto(s)
Bacterias/clasificación , Biopelículas , Agua Dulce/microbiología , Nitrificación , Aguas del Alcantarillado/microbiología , Amoníaco/metabolismo , Bacterias/aislamiento & purificación , Bacterias/metabolismo , Hibridación Fluorescente in Situ , Nitritos/metabolismo , Nitrosomonas/genética , Nitrosomonas/aislamiento & purificación , Oxidación-Reducción , Oxidorreductasas/genéticaRESUMEN
Dispersal and colonization are important for the assembly and biodiversity of microbial communities. While emigration as the initial step of dispersal has become increasingly understood in model bacterial biofilms, the drivers of dispersal and colonization in complex biofilms remain elusive. We grew complex biofilms in microcosms from natural surface water in laminar and turbulent flow, and investigated dispersal and colonization patterns of fluorescently labeled cells and microbeads in nascent and mature biofilms. Settling occurred in nonrandom spatial patterns governed by the interplay of local flow patterns and biofilm topography. Settling was higher in treatments with nascent biofilms, with fewer cells remaining in the water column than in treatments with mature biofilms. The flow regime had no effect on settling velocity, even though in mature biofilms the formation of streamers under turbulent flow enhanced particle trapping compared with the laminar flow treatment. Hence, small-scale variations in the flow pattern seemed to be more important than the overall flow regime. Furthermore, spatial analysis of the colonizer patterns suggests that bacteria have moved in the biofilm after settling. Our results show that colonization of biofilms in a model stream environment is a heterogeneous process differently affected by biological and physical factors.
Asunto(s)
Bacterias/crecimiento & desarrollo , Biopelículas/crecimiento & desarrollo , Ríos/microbiología , Biodiversidad , Ecosistema , Microesferas , Movimientos del AguaRESUMEN
Riparian zones are hotspots of plant species richness in temperate and boreal biomes. The phenomenon is believed to be caused primarily by river-related processes, and upland influences on riparian zones have received relatively little attention. We investigated the importance of discharge of groundwater derived from uplands on riparian patterns in vascular plant species composition. We found that groundwater discharge areas in riparian zones were 36-209% more species rich than non-discharge areas, depending on spatial scale (1-50 m wide transects from annual high-water levels to summer low-water levels) and river (one free-flowing and one regulated). Higher nitrogen availability and less drought stress during low river stages are suggested as the major causes for the higher species diversity in discharge areas. Riparian zones lacking groundwater discharge lost more species following water-level regulation than did discharge areas. This indicates that groundwater discharge areas are more resistant to regulation because both individual plants and plant populations may grow larger in discharge areas. These results demonstrate that riparian zones are controlled by water and nutrient input from upland parts of catchments in ways that have been overlooked despite more than three decades of research into linkages between stream ecosystems and their valleys.